Mass extinctions have served as huge reset buttons that dramatically changed the diversity of species found in oceans all over the world, according to a comprehensive study of fossil records. The findings suggest humans will live in a very different future if they drive animals to extinction, because the loss of each species can alter entire ecosystems.
Some scientists speculate that effects of humans are fueling another great mass extinction. A few go so far as to say we are entering a new geologic epoch, leaving the 10,000-year-old Holocene Epoch behind, marked by major changes to global temperatures and ocean chemistry, increased sediment erosion, and changes in biology that range from altered flowering times to shifts in migration patterns of birds and mammals and die-offs of tiny organisms that support the entire marine food chain.
Looking back in time, the diversity of large taxonomic groups mostly hovered around a certain equilibrium point that represented a diversity limit of species’ numbers. That diversity limit also appears to have changed spontaneously throughout about every 200 million years.
How today’s extinction crisis (species today go extinct at a rate that may range from 10 to 100 times the so-called background extinction rate) may change the face of the planet and its species goes beyond what humans can predict.
The findings revealed various examples of diversity shifts, including one that took place in a group of ocean bottom-dwelling bivalves called brachiopods, which are similar to clams and oysters. They dominated the Paleozoic era from 540 to 250 million years ago, and branched out into new species during two huge adaptive spurts of growth in diversity–each time followed by a big crash.
The brachiopods then reached a low, but steady, equilibrium over the past 250 million years in which there wasn’t a surge or a crash in numbers, and still live on today as a rare group of marine animals.
Nothing lasts forever…
That means today’s species matter for environments around the world, and humans can’t simply expect replacements from the diverse species of the future.
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